Modbus Communication issues

[EngYoug006]

Hi everyone,

We are constantly facing communication loss between Modbus Devices (TeSys, ATS48, PM8000, SEPAM...) and PLC (M580 Hotstanby) in our Ecostruxure Hybrid DCS system ,  with recurrent following alarms for instance; Device warning, Device Failure, Comm Error, ... (refer to Alaram File.pdf). Note that this issue occurs on different zones, devices stop randomly which increases plant downtime. 

We explored and checked many possibilities  (Earthing, harmonics, made some software changes on both filed and PLC side: Hybrid DCS template and DFBs;  Egx Gateways settings or eNOC port settings; hardware issues such as cables, gateways or switches... see COM Diagnostics.pdf )but still couldn't solve the problem.

Thank you

[Hennie_Smith]

Have you checked the 24Vdc on the equipment including network switches? I had it in the past if the V drop just enough, I got comms errors. Measure at the end in the MCC furthest from the power supply. Are your motor starter contactors coils AC or 24Vdc since on the 24Vdc coils, the power drawn to energize these contactors are quite high.

[EngYoug06]

We checked everything and issues don't come from the 24Vdc.

[Siddiqui]

I am not an expert on hybrid DCS, but I can provide the following comments on the network side.

Can you please check the network status? Ensure the network is stable and there is no storm inside the network.

Additionally, you can capture the packets and perform the Wireshark analysis to get more insight into details.

From the shared snapshot of the eNOC messaging, I can see there are errors.

From the M580 point of view, the BMENOC module scans all the devices. So, you can configure Port 1 (Service Port) of the BMENOC0301/X module as a Mirror port and capture the packets.

The capture provides details on what is going on at that network level. You can also track down the analysis at the device level. Which devices are not responding to the requests? Or is the scanning rate much faster than the device's response capability?

Wireshark analysis requires expertise. If you can do it, it's good. Otherwise, please create a ticket with the support team providing all the investigation details.

I hope the above comments provide help.                                                          

[EngYoug06]

@Siddiqui Thank you so much for your help. We performed all of the described checkings as well as the creation of a ticket. After having tried most of recommendations we decided to replace gateways by M241 PLC and it seems to have brought enhancements and considerably decreased errors.